According to the sources, Osteoporosis is an age-related disorder specifically characterised by decreased bone mass and increased chances of fractures . The other options are incorrect based on the following facts: Muscular dystrophy is a progressive degeneration of skeletal muscle mostly due to a genetic disorder, not age-related shortening ; Myasthenia gravis is an autoimmune disorder that affects the neuromuscular junction, leading to fatigue and paralysis, rather than directly inhibiting filament sliding ; and Gout is the inflammation of joints caused by the accumulation of uric acid crystals, not calcium deposition .